The invention relates to marine jet drives. More particularly, the invention relates to a self-activating weed grate to be used on a marine jet drive that effectively allows the weed grate to be cleaned out during operation.
Jet propelled watercraft have a number of significant advantages over propeller-type watercraft. One of the advantages of jet propulsion units is that they permit the watercraft to be operated in very shallow bodies of water as compared to a conventional propeller-driven unit, since a jet propulsion unit does not include the lower unit and propeller of a conventional propulsion unit which extend below the hull of the boat.
Jet propulsion units for watercraft typically have an engine-driven jet pump located within an intake duct in the hull of the watercraft. An inlet opening through the underside of the watercraft allows seawater to flow to the pump in the intake duct. A water intake housing is adapted to the hull on the bottom of the watercraft and closes off the bottom of the watercraft while allowing seawater to pass through the inlet opening into the intake duct and to the jet pump. The jet pump generally consists of an impeller and a stator located within the intake duct followed by a nozzle. The impeller of the pump is driven by the engine, and provides energy to the flow of seawater to the pump. From the impeller, the seawater flows through the stator and the nozzle before exiting rearward through a vectored outlet to steer the watercraft (e.g., a generally tubular rudder that can rotate to steer the watercraft).
When operating a watercraft including a jet propulsion unit in shallow bodies of water, it is possible to ingest seaweed and other debris into the jet propulsion unit through the inlet opening. To prevent debris from entering through the inlet opening, a grate or screen is typically placed across the inlet opening.
Marine jet drive intake grates are known in the prior art. As mentioned, the intake grate or screen is provided across the water inlet opening of the jet propulsion unit to prevent large pieces of debris from being drawn into the jet propulsion unit and damaging the impeller and the various other internal components. During continuous use of the marine jet drive in relatively weedy areas, the large amount of floating weeds can cause the intake grate to become clogged. The suction created by the impeller causes weeds and debris to wrap around the tines of the intake grate and slide rearwardly along the tines, where the weeds become stuck at the juncture between the tines and the aft end of the intake grate. When a significant amount of weeds and other debris builds up, the dense mass prevents water from flowing through the intake grate into the jet drive. This reduced amount of water flow can cause the jet drive to stall and require the user to remove the weeds and debris caught in the intake grate.
One solution to the problem of weeds clogging the intake grate is shown in Chartier U.S. Pat. No. 5,577,941. In this patent, the individual tines of the intake grate have end tips which are spaced from the aft end of the intake grate by a pass-through gap. Thus, when weeds and debris become intertwined between the tines, the weeds are able to slide rearwardly along the tines and through the gap while the jet drive is operating. In this manner, the problem of clogging has been reduced. However, the size of the gap between the end tips of the tines and the aft end of the weed grate plate limits the size and amount of weeds that can pass through the gap and through the jet drive. Thus, large clumps of weeds which have a thickness greater than the gap between the tines and the aft end of the intake grate can cause clogging of the intake grate.
Therefore, it can be appreciated that a jet drive weed grate which prevents large debris from passing therethrough during normal operating conditions, while allowing weeds which begin to clog up the grate to pass through the jet drive would be a desirable improvement in the jet drive marine propulsion field.